The primary objective of this project is to develop psychophysical testing techniques to analyze pain perception in monkeys which have direct applications for the study of pain in man. We are developing an approach based on signal detection theory to provide two independent measures of pain-elicited behavior. The first is called d' and is an index of pain perception while the second is called beta and is an index of response bias which is a measure of general reactivity to stimuli. So far we have shown that neither valium nor morphine affect d' but valium significantly alters response bias. Only Xylocaine was effective in changing d'. We are now planning to extend these studies to include analysis of the effects of other drugs, brain stimulation and brain ablation on d' and response bias.